Field of the Invention
The present disclosure relates to a printing element substrate, a liquid ejection head, and a printing apparatus.
Description of the Related Art
Some liquid ejection heads, for example, an ink-jet print head that ejects ink to print an image, use an electrothermal conversion element (a heater) or a piezoelectric element as a printing element for generating ejection energy. Such an ink-jet print head applies driving voltage to a printing element and ejects ink from ejection ports using the ejection energy generated from the printing element. Since the amount of ink ejected from the ejection ports changes according to the driving voltage applied to the printing element, it is important to stabilize the driving voltage to stabilize liquid ejection characteristics. Japanese Patent Laid-Open No. 2010-155452 discloses a configuration in which the gate voltage of a PMOS transistor connected to one end of each heater and the gate voltage of an NMOS transistor connected to the other end of the heater are individually controlled by individual voltage conversion circuits. The voltage conversion circuits, the PMOS transistor, the NMOS transistor, and the heater are provided on a print head substrate. PMOS is an abbreviation of a p-channel metal-oxide semiconductor, and NMOS is an abbreviation of an n-channel metal-oxide semiconductor.
However, the print-head substrate disclosed in Japanese Patent Laid-Open No. 2010-155452 has two transistors for each of the plurality of heaters. This increases the number of heaters to increase the area of a substrate on which the transistors are disposed, thus making it difficult to achieve size reduction of the substrate.
In contrast, Japanese Patent Laid-Open No. 2015-189049 discloses a print-head substrate having a first transistor that forms an electrical pathway common to a plurality of heaters and a plurality of second transistors that independently drive the plurality of heaters. In other words, this print-head substrate has the first transistor shared by a plurality of heaters, while having a plurality of transistors for one heater. This stabilizes the liquid ejection characteristics, while allowing the substrate to be smaller than a configuration in which the number of first transistors and the number of second transistors are the same as the number of heaters.
However, the liquid ejection characteristics of the print-head substrate disclosed in Japanese Patent Laid-Open No. 2015-189049 can sometimes become unstable. Specifically, if a printing element, such as a heater, is broken, a wiring line connected from the first transistor to the printing element can corrode into breakage. This can make the liquid ejection characteristics unstable because not only driving voltage applied to the broken printing element but also driving voltage applied to another printing element connected to the same first transistor as that connected to the broken printing element can drop or stop.